A CVT is a uniform-motion transmission in which the ratio of the rotational speeds of the driving shaft and of the driven shaft, the transmission ratio, can assume an infinite number of values (stages) in a certain range. This may also include the standstill state or the rotational direction reversal of a shaft. The transmission of the movement takes place via a non-rigid coupling of components, the geometries of which determine the transmission action according to the lever principle. A change in transmission ratio is obtained by a change in the component geometries, which however at the same time cannot take place without a change in the geometries at the location of the component coupling.
Numerous freewheel devices for crank-type CVTs have, for this purpose, clamping bodies which are arranged between an inner ring, which is formed by a region of the drive output shaft, and an outer ring. Here, the surfaces of the outer ring and of the inner ring are coordinated with one another such that, in one direction of relative rotation between the inner ring and outer ring, the clamping bodies can block the rotation, such that the outer ring and the inner ring are rotated together. In the other direction of relative rotation between the outer ring and the inner ring, no blocking action is effected by the clamping bodies. The individual clamping bodies are loaded in the blocking direction, which may be realized by means of at least one spring element.
A crank-type CVT having roller-shaped clamping bodies is known, for example, from EP 1 650 071 A2. The rollers are forced into the gap between the inner star and the outer ring by a spring as a pressure-exerting, element and, as a result of which, the rollers, as clamping elements, are held in contact with the outer ring and inner star. Here, a cage is provided for the rollers. Here, the spring may be designed as a leg spring where the switching action is attained by virtue of the spring or the leg spring performing a pivoting movement, which causes the roller to be pushed from the right flank, which is associated therewith, onto the left flank.
DE 102 43 533 A1 describes a switching device which serves for switching the blocking function of the freewheel. The switching device comprises a plurality of switching units arranged between adjacent rotationally symmetrical clamping bodies. The switching units can be actuated synchronously and have switching means which have a rotatable disk-shaped region and also a profiled region composed preferably of a profiled bar. The profiled region has a leg spring, which can be braced between the profiled region and a clamping body. For this purpose, the leg spring has a leg which can load a clamping body in the corresponding blocking direction.
The spring-loading and damping (for example, as per DE 693 26 387 T2) may furthermore be realized by so-called Z-springs which are supported at one side on the radially outer surface of the clamping body and at the other side on a contact surface of the cage.
Also known is the use of Z-springs which, in the damping position, act with one leg on the radially outer region of a clamping body and with a second leg on the radially inner region of an adjacent clamping body where in the maximum pivoting position, there is no longer contact between the first leg and the clamping body.
The abovementioned solutions have the disadvantage that, as a result of the single-acting leg springs, the damping and centrifugal force compensation cannot be fully utilized, or that the compensation can be achieved only with a large loss in efficiency, or that, with the Z-springs, there is the risk of lifting of the clamping bodies at full torque. A further disadvantage of the design is that the Z-springs require a greater amount of installation space, which can be is compensated for by reducing the number of clamping bodies, but this in turn reduces the load capacity.